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Employee Future Benefits - Defined Benefit Obligation (Details) - CAD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Defined benefit obligation, beginning of period | $ 278 |  |
Current service cost | 8 | $ 10 | $ 12
Actuarial gain arising from demographic assumptions | (11) | (26) |
Defined benefit obligation, ending of period | 294 | 278 |
Present value of defined benefit obligation |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Defined benefit obligation, beginning of period | 664 |  |
Interest cost | 20 | 23 | 22
Defined benefit obligation, ending of period | 675 | 664 |
Registered |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Defined benefit obligation, beginning of period | 170 |  |
Current service cost | 5 | 7 | 9
Defined benefit obligation, ending of period | 175 | 170 |
Registered | Present value of defined benefit obligation |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Defined benefit obligation, beginning of period | 543 | 514 |
Current service cost | 5 | 7 |
Interest cost | 16 | 19 | 18
Benefits paid | (45) | (51) |
Curtailment and amendment gain | (2) | (3) |
Actuarial gain arising from demographic assumptions | 0 | 0 |
Actuarial loss arising from financial assumptions | 43 | 57 |
Actuarial gain (loss) arising from experience adjustments | (17) | 2 |
Effect of translation on US plans | (1) | (2) |
Defined benefit obligation, ending of period | 542 | 543 | 514
Supplemental Pension Plan |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Defined benefit obligation, beginning of period | 86 |  |
Current service cost | 2 | 2 | 2
Defined benefit obligation, ending of period | 95 | 86 |
Supplemental Pension Plan | Present value of defined benefit obligation |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Defined benefit obligation, beginning of period | 99 | 80 |
Current service cost | 2 | 2 |
Interest cost | 3 | 3 | 3
Benefits paid | (5) | (4) |
Curtailment and amendment gain | 0 | 0 |
Actuarial gain arising from demographic assumptions | 0 | 0 |
Actuarial loss arising from financial assumptions | 10 | 9 |
Actuarial gain (loss) arising from experience adjustments | 0 | 9 |
Effect of translation on US plans | 0 | 0 |
Defined benefit obligation, ending of period | 109 | 99 | 80
Other |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Defined benefit obligation, beginning of period | 22 |  |
Current service cost | 1 | 1 | 1
Defined benefit obligation, ending of period | 24 | 22 |
Other | Present value of defined benefit obligation |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Defined benefit obligation, beginning of period | 22 | 25 |
Current service cost | 1 | 1 |
Interest cost | 1 | 1 | 1
Benefits paid | (1) | (1) |
Curtailment and amendment gain | 0 | 0 |
Actuarial gain arising from demographic assumptions | 0 | (2) |
Actuarial loss arising from financial assumptions | 2 | 2 |
Actuarial gain (loss) arising from experience adjustments | 0 | (4) |
Effect of translation on US plans | (1) | 0 |
Defined benefit obligation, ending of period | 24 | 22 | 25
Total | Present value of defined benefit obligation |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |
Defined benefit obligation, beginning of period | 664 | 619 |
Current service cost | 8 | 10 |
Interest cost | 20 | 23 |
Benefits paid | (51) | (56) |
Curtailment and amendment gain | (2) | (3) |
Actuarial gain arising from demographic assumptions | 0 | (2) |
Actuarial loss arising from financial assumptions | 55 | 68 |
Actuarial gain (loss) arising from experience adjustments | (17) | 7 |
Effect of translation on US plans | (2) | (2) |
Defined benefit obligation, ending of period | $ 675 | $ 664 | $ 619

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- Definition The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from changes in demographic assumptions that result in remeasurements of the net defined benefit liability (asset). Demographic assumptions deal with matters such as: (a) mortality; (b) rates of employee turnover, disability and early retirement; (c) the proportion of plan members with dependants who will be eligible for benefits; (d) the proportion of plan members who will select each form of payment option available under the plan terms; and (e) claim rates under medical plans. [Refer: Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 141 -Subparagraph c -Clause ii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_141_c_ii&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from changes in financial assumptions that result in remeasurements of the net defined benefit liability (asset). Financial assumptions deal with items such as: (a) the discount rate; (b) benefit levels, excluding any cost of the benefits to be met by employees, and future salary; (c) in the case of medical benefits, future medical costs, including claim handling costs (ie the costs that will be incurred in processing and resolving claims, including legal and adjuster's fees); and (d) taxes payable by the plan on contributions relating to service before the reporting date or on benefits resulting from that service. [Refer: Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 141 -Subparagraph c -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_141_c_iii&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The increase (decrease) in the net defined benefit liability (asset) resulting from employee service in the current period. [Refer: Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 141 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_141_a&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The decrease (increase) in the net defined benefit liability (asset) resulting from the gain (loss) on changes in the effect of limiting a net defined benefit asset to the asset ceiling, excluding amounts included in interest income or expense. [Refer: Interest income; Net defined benefit liability (asset); Interest expense (income), net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 141 -Subparagraph c -Clause iv -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_141_c_iv&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The increase (decrease) in the net defined benefit liability (asset) resulting from changes in foreign exchange rates. [Refer: Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 141 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_141_e&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The increase (decrease) in the net defined benefit liability (asset) resulting from the passage of time. [Refer: Interest expense; Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 141 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_141_b&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The amount of deficit or surplus in a defined benefit plan, adjusted for any effect of limiting a net defined benefit asset to the asset ceiling. [Refer: Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 140 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_140_a&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The decrease (increase) in the net defined benefit liability (asset) resulting from payments from the plan in respect of settlements. [Refer: Gains (losses) arising from settlements, net defined benefit liability (asset); Net defined benefit liability (asset); Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 141 -Subparagraph g -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_141_g&doctype=Standard -URIDate 2019-03-27 + Details
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